Am 06.03.2025 um 11:33 hat Kevin Wolf geschrieben: > Am 04.03.2025 um 16:52 hat Alberto Faria geschrieben: > > Avoid emulating FUA when the driver supports it natively. This should > > provide better performance than a full flush after the write. > > > > Signed-off-by: Alberto Faria <afa...@redhat.com> > > Did you try out if you can see performance improvements in practice? > It's always nice to have numbers in the commit message for patches that > promise performance improvements.
I was curious enough to see how this and the recent series by Stefan (virtio-scsi multiqueue) and myself (FUA on the backend + polling improvements) play out with virtio-scsi, so I just ran some fio benchmarks with sync=1 myself to compare: iops bs=4k cache=none | virtio-scsi | virtio-blk | O_SYNC workload | qd 1 | qd 16 | qd 1 | qd 16 | --------------------------------+---------+---------+---------+---------+ master | 21296 | 109747 | 25762 | 130576 | + virtio-scsi multiqueue | 28798 | 121170 | - | - | + FUA in scsi-disk | 51893 | 204199 | - | - | --------------------------------+---------+---------+---------+---------+ Total change | +143.7% | +86.1% | - | - | (No new numbers for virtio-blk because virtio-scsi patches obviously don't change anything about it. Also no numbers for FUA in file-posix because it's unused with cache=none.) iops bs=4k cache=directsync | virtio-scsi | virtio-blk | O_SYNC workload | qd 1 | qd 16 | qd 1 | qd 16 | --------------------------------+---------+---------+---------+---------+ master | 32223 | 109748 | 45583 | 258416 | + FUA in file-posix + polling | 32148 | 198665 | 58601 | 320190 | + virtio-scsi multiqueue | 51739 | 225031 | - | - | + FUA in scsi-disk | 56061 | 227535 | - | - | --------------------------------+---------+---------+---------+---------+ Total change | +74.0% | +107.3% | +28.6% | +23.9% | Of course, the huge improvements on the virtio-scsi side only show how bad it was before. In most numbers it is still behind virtio-blk even after all three patch series (apart from cache=none where the availability of FUA on the device side makes a big difference, and I expect that virtio-blk will improve similarly once we implement it there). Also note that when testing the virtio-scsi multiqueue patches, this was still a single iothread, i.e. I wasn't even making use of the new feature per se. I assume much of this comes from enabling polling because the series moved the event queue handling to the main loop, which prevented polling for virtio-scsi before. The series also got rid of an extra coroutine per request for the blk_is_available() call in virtio_scsi_ctx_check(), which might play a role, too. Anyway, I like these numbers for FUA in scsi-disk. It makes write back cache modes almost catch up to write through with O_SYNC workloads. We should definitely get this merged and do the same for virtio-blk. Kevin
